The present invention is concerned with hot melt compositions which are especially but not solely useful as (A) adhesives for the backsizing of carpets, including tufted carpets, and (B) as hot melt pressure sensitive adhesives. More particularly the present invention is concerned with hot melt compositions which are substantially free of wax.
A. Tufted carpets are composite structures in which the yarn forming the pile, i.e., the surface of the carpet, is needled through a base fabric whereby the base of each tuft extends through the base fabric and is visible on the bottom surface. Tufted carpets are generally of two types, the first being the type commonly known as a "nap" carpet where the yarn loops are formed by needling or punching a continuous yarn just through the base fabric, thus forming the base of the carpet, while the tops of the loops are generally one-fourth inch to three-quarters inches long thus forming the wearing surface of the carpet. The second type of tufted carpet, commonly known as a "shag" carpet, has the same base as the "nap" carpet but the tops of the loops have been split or the tips of the loops have been cut off. The surface of the "shag" carpet is thus formed by the open ends of the numerous U-shaped pieces of yarn -- the base of the U being embedded in the base fabric.
The loops of yarn are needled through and embedded in the base fabric (the combination of which is the raw tufted carpet) thus forming the tufted base, which must be secured to the base fabric to prevent the loops from being pulled out of the base fabric. The tufted bases are generally secured by applying an adhesive to the back of the raw tufted carpet to bond the tufted yarns to the base fabric. A secondary backing material is usually also applied to the back of the raw tufted carpet and bonded thereto with the same adhesive that bonds the yarn to the base fabric. The application of the secondary backing material further secures the loops of yarn since the loops of yarn are then bonded by the adhesive to the backing material as well as the base fabric.
The yarn used in forming the pile of a tufted carpet can be made of any type of fiber known in the art to be useful for tufted carpets, e.g., nylon, acrylics, wool, cotton, rayon and the like.
The base fabric or primary backing may be of any type known in the art and may be woven, for example, woven jute, woven slit polypropylene film, burlap, and the like, or may be non-woven fabric, e.g., needle punched, non-woven polypropylene web. Likewise, the secondary backing material may be of any type known in the art, e.g., woven jute, woven slit polypropylene film, burlap, foam material such as polyurethane foams or blown vinyl film and non-woven fabrics such as needle punched, non-woven polypropylene web, or blends of polyesters and polypropylene.
In preparing such tufted carpets, the adhesives are usually applied to the primary backing which holds the tufted matrix in the form of a latex. A secondary backing is then usually applied to the carpet. The carpet is then heated to cure the latex to ensure a bond between the latex and the tufted carpet, and the latex and the primary and secondary backings. This curing or drying of the latex is quite time consuming, expensive, and often leads to rejects because of insufficient curing during the process. In addition, overheating of the carpet may occur during the curing which in turn may affect the shade of the carpet.
In addition to the use of latex as an adhesive carpet backing, recently there has been some activity in the use of hot melt adhesives as carpetbackings or sizing adhesives. For example, such hot melt adhesives have been based upon compositions containing copolymers of ethylene and vinyl acetate admixed with a wax such as paraffin wax or microcrystalline wax. For example, U.S. Pat. No. 3,390,035 discloses a hot melt adhesive consisting essentially of from 90 to 10% by weight of an ethylene/vinyl acetate copolymer and from 90 to 10% by weight of a wax. Such hot melt adhesives however exhibit incompatibility and sometimes separation upon cooling of the hot melt. In addition, such compositions have not demonstrated the degree of flexibility and adhesive strength desired by the carpet industry.
B. Pressure sensitive adhesives are one of the most widely used types of adhesives made today. Consequently a large volume of products using such adhesives are manufactured each year. The conventional pressure sensitive adhesives are made and applied in a solvent solution, necessitating the extensive use of solvents. The use of solvents is undesirable for a number of reasons. First, solvent based pressure sensitive adhesive production involves an inherent hazard of flamability of the adhesive. Second, in the production of such adhesives, special equipment is necessary to rapidly and efficiently remove the solvents from the products after the adhesive has been applied. Third, the use of large amounts of solvent increases the likelihood of pollution in areas where large amounts of adhesives are being produced. Finally, many potential materials to which the adhesive could be applied will be adversely affected by certain solvents. Thus solvent based pressure sensitive adhesives are unduly limited in use by the presence of the solvent.
For these and other reasons, the development of an effective pressure sensitive adhesive which requires little or no solvent in the manufacturing process is highly desirable.
Because of the application requirements of pressure sensitive adhesives, it is necessary, in formulating same to consider not only the adhesiveness but also the cohesiveness of the composition.